Process for reducing trivalent titanium content in slag

ABSTRACT

A process for reducing the content of trivalent titanium in solid titaniferous materials comprises controlled heating of the material.

Unite States Patent 1 [11] 3,868,441 Agee et al. Feb. 25, 1975 [54] PROCESS FOR REDUCING TRIVALENT 2,980,508 4/1961 Moklebust et a1. 423/82 IN 2,990,250 6/1961 Moklebust et al.. 423/82 7 I R S E Z 2 M I 3,739,061 6/1973 Stickney et a1. 423/610 J] mentors g fg gf f of FOREIGN PATENTS OR APPLICATIONS La, 2,038,247 3/1971 Germany 423/610 [73] Assignees Ethyl Corporation, Richmond, Va. OTHER PUBLICATIONS Jelks Barksdale Book, Titanium," Second Ed., 1966, [22] Flled' May 1973 pages 209, 234-236. The Ronald Press Co., New [21] Appl. No.: 356,433 York.

Primary ExaminerEdward Stern 52 U.S. Cl 423 6 423 2, 423 1 l 9 42 2 Attorney, Agent, or Fzrm--Donald L. Johnson; John F. 51 Im. Cl C04g 23/00, (:01 g 23/04 Seberth; Edgar splelman [58] Field of Search 423/71, 610, 611, 615,

423/616, 69, 82 [57] ABSTRACT A process for reducing the content of trivalent tita- [56] Refe ces Cit d nium in solid titaniferous materials comprises con- UNITED STATES PATENTS trolled heating of the material.

2,589,910 3/1952 Schneider 423/82 6 Claims, N0 Drawings PROCESS FOR REDUCING TRIVALENT TITANIUM CONTENT IN SLAG BACKGROUND OF THE INVENTION In order to obtain high grade titanium dioxide concentrates from titaniferous ores it is necessary to remove a substantial portion of the iron values therefrom. In commercial operations removal of iron values is usually achieved by a thermo-reduction treatment of the titaniferous ore which reduces the iron to a metallic state thus making it easily removable from the titanium values. After the iron is removed a titanium-containing concentrate is recovered; this concentrate is generally referred to in the industry as titaniferous slag. This slag, however, is still not suitable as feed to certain TiO pigment-producing processes due to the slag having high concentrations of trivalent titanium, i.e., Ti 3. The high concentration of trivalent titanium is due in large part to the above mentioned iron-removing thermoreduction process as this process reduces, along with the iron, a portion of the tetravalent titanium in the titaniferous ore to trivalent titanium. Processes which rely on digestion of the slag in sulfuric acid to produce pigmentary grade TiO are especially not suited to using a feed containing large amounts of trivalent titanium as large amounts of noxious SO are evolved from the process. Such evolution presents disposal problems.

Trivalent titanium concentrations in titaniferous slags can be reduced by oxidation of the trivalent titanium to tetravalent titanium prior to feeding the slag to the mineral acid processes. Generally speaking, oxidation is achievable by direct and continuous heating the slag to a temperature in excess of 450C in the presence of oxygen. However, this procedure, though it reduces trivalent titanium content, results in the undesirable production of a substantial amount of rutile especially when the reduction of the trivalent titanium content approaches 20 percent of the total titanium. Therefore achieving low trivalent titanium concentrations by this process is penalized by rutile formation. Rutile formation is undesirable as the rutile is substantially insoluble in the H 80, and thus the titanium values are lost.

Therefore it is an object of this invention to provide a process for reducing the content of trivalent titanium in solid titaniferous materials without the attendant formation of substantial amounts of rutile.

This invention relates to a process for reducing the content of trivalent titanium in trivalent titaniumcontaining solid titaniferous material without the attendant formation of significant amounts of rutile which comprises: applying heat to the titaniferous material in the presence of oxygen until the exothermic oxidation of the trivalent titanium is initiated; discontinuing the application of heat at that initiation point so that the temperature of the titaniferous material continues to rise due to the heat generated by the exothermic oxidation of the trivalent titanium; and reapplying heat to the titaniferous material after the temperature of the material reaches a maximum, indicating a reduction of the oxidation reactivity of the material, whereby the temperature of the titaniferous material is raised and maintained within a range of from about 300C to about 450C until the desired reduction of the trivalent titanium content is achieved.

By practicing the process of this invention the practitioner is able to greatly reduce the content of trivalent titanium in the slag, i.e., down to about percent of the titanium as trivalent titanium, without the attendant formation of significant amounts of rutile-indeed the rutile formed is less than about 3.0 weight percent. Not only does the process of this invention achieve these excellent results, it is also the paragon of simplicity when compared to prior art processes in which the slag is subjected to various and sundry treatments requiring complicated equipment and process procedures. For example, U.S. Pat. No. 2,980,508 teaches that the trivalent titanium content can be reduced by wetting the slag with electrolytes prior to the heating thereof. Such a procedure is difficult at best as it is not always easy to control the amount of wetting which is desired. Other processes having complicated procedures are U.S. Pat. No. 2,990,250, which forms agglomerates of finely divided concentrates; and U.S. Pat. No. 2,589,910 which requires a porous cake formed by sulfuric acid and the slag.

The initial heating of the trivalent titanium containing titaniferous slag in the process of this invention is for the purpose of raising the slag temperature so that the trivalent titanium will begin to oxidize to tetravalent titanium. The slag temperature at which oxidation initiation occurs is about C. This initial heating, as is the entire process, is done in the presence of oxygen. Either pure oxygen or an oxygen-containing gas such as air will suffice. Air is preferred as it is readily available and economical.

After the initial point of oxidation has been reached the application of heat to the slag is discontinued. The oxidation of the trivalent titanium, however, being exothermic, will continue. The heat generated by the exothermic oxidation will also cause the slag temperature to rise to a temperature within the range of from about to about 300C depending upon the reactivity of the slag-the higher the activity the higher the temperature rise. After attainment of a maximum slag temperature within this temperature rangesuch attainment indicating a reduction in oxidation reactivityheat is reapplied to the titaniferous slag to raise and maintain the slag temperature within the range of from about 300 to about 450C. It has been discovered that a preferred temperature range for slag having a particle size of 80 percent through 325 mesh is from about 350 to about 400C. Reapplication of heat is delayed until a reduction in oxidation reactivity is realized so as to prevent over-heating of the material which would result in rutile formation. The slag is maintained within this temperature range until thecontent of trivalent titanium is reduced to 10 to 20 percent or as desired. For example, if the titaniferous material has a particle size of 80 percent through 325 mesh then I to 5 hours is sufficient to achieve less than 20 percent Ti 3. Larger sizes require longer periods which can be easily determined by sampling and analyzing the treated slag during the maintenance period. Maintaining the temperature of the slag in excess of 450C is not desirable as rutile formation is accelerated.

After being treated by the process of this invention the treated slag may be allowed to cool to a temperature which is suitable for subsequent treatment, e.g., pigmentary grade TiO producing processes.

The entire process of this invention can be carried out in very simple equipment. It has been found that particularly good results can be obtained by carrying out the process of this invention in a rotary kiln. However other modes can be utilized such as by the use of niferous slag temperature can be readily determined by those skilled in the art.

As mentioned previously, titaniferous slag is generally de'fined in the industry as that slag which results from the the'rmo-reduction of titaniferous ores for the removal of iron values therefrom. This thermoreduction of the titaniferous ores can be achieved in smelting furnaces which raise the temperature of the ore to the reduction temperature of the iron values in the presence of a reductant such as carbon.

For the process of this invention the slag is preferably crushed or ground so that slag size is from about 325 to about 4 mesh. A highly preferred size is slag having at least 75 percent through 325 mesh. By utilizing slag of small size it has been found that the period for carrying out the process of this invention is shortened in relation to the period of time-required by slag having a large size. Crushing of the slag can be accomplished by ball milling, roller milling, etc.

It is to be understood that trivalent titanium containing titaniferous material other than titaniferous slag can be successfully treated bythe process of this invention.

Exemplary of such materials is titaniferous concentrates obtained from rotary kilns in which the iron is reduced without smeltering or sintering the material. After such treatment, the iron is separated by mechanical or magnetic means.

The following examples are given to further illustrate the process of this invention and are not intended to be a limitation thereon.

For the following examples the titaniferous slag to be treated was prepared by-smelting titaniferous ore in the presence of carbon in an electric arc furnace maintained at a temperature within a range of from about 1400Cto about l800C. Two layers are formed, one of iron and the other of slag. The two layers are then separately tapped to achieve separation of the iron layer from the slag layer.

Determination for Ti 3 content, expressed as percent titanium as Ti 3, was achieved by the analytical method entitled Determination of Titanium and Iron in Titaniferous Slags found in Scotts Standard Methods of Chemical Analysis, 6th Edition, Vol. 1, pp 1118, P. Van Norstrand Co.

Rutile content expressed in weight percent, based upon total slag weight, was determined by X-ray defraction.

EXAMPLE I Titaniferous slag containing 49.0% Ti 3 was crushed so that 80% would pass through 325 mesh. The ground slag was fed to a rotary kiln equipped with an iron constantan thermocouple in its interior for contacting the crushed slag and thus monitoring its temperature. Heat was applied to the crushed slag by a gas-fed flame under the kiln until a temperature of about 150C was achieved. At this point the gas flame was greatly reduced so that it effectively no longer heated the slag.

The temperature of the slag was monitored until a maximum temperature was realized and the temperature began to remain constant. At this point the gas flame was intensified so as to reapply heat to the crushed slag and to raise and maintain its temperature at 350C for 150 minutes. After this period the slag was allowed to cool and was analyzed. The Ti 3 content was reduced to 14.9% while the rutile content was only 1.4 weight percent.

EXAMPLE ll The procedure of Example I was repeated except that the initial Ti 3 content was 49.8% and the temperature during the reapplied heat period was 400C and the period was 105 minutes. Analysis of the treated slag showed that the Ti 3 content was reduced to 15.1% while the rutile content was only 2.3 weight percent.

EXAMPLE III The procedure of Example I was repeated except that the initial Ti 3 content was 53.7% and the temperature during the reapplied heat period was 430C and the period was minutes. Analysis of the treated slag showed that the Ti 3 content was reduced to 26.0% while the rutile was only 1.6 weight percent.

In all of the above examples oxygen was provided by air.

What isclaimed is:

l. A process for reducing the content of trivalent titanium in trivalent titanium-containing solid titaniferous slag which comprises:

a. applying heat to the titaniferous slag in the presence of oxygen until the exothermic oxidation of the trivalent titanium is initiated, that is at a slag temperature of about 150C, and discontinuing the application of heat at that initiation point so that the temperature of the titaniferous slag continues to rise due to the heat generated by the exothermic oxidation of the trivalent titanium; and

b. reapplying heat to the titaniferous slag after the temperature of the slag reaches a maximum, whereby the temperature of the titaniferous slag is maintained within a range of from about 300C to about 450C until the desired reduction of the trivalent titanium contents is achieved.

2. The process of claim 1 wherein the oxygen is provided by air.

3. The process of claim 1 wherein the titaniferous slag has a particle size within the range of from about 4 to about 325 mesh.

4. The process of claim 1 wherein the titaniferous slag has a particle size of at least percent-325 mesh. 

1. A PROCESS FOR REDUCING THE CONTENT OF TRIVALENT TITANIUM IN TRIVALENT TITANIUM-CONTAINING SOLID TITANIFEROUS SLAG WHICH COMPRISES: A. APPLYING HEAT TO THE TITANIFEROUS SLAG IN THE PRESENCE OF OXYGEN UNTIL LTHE EXOTHERMIC OXIDATION OF THE TRIVALENT TITANIUM IS INITIATED, THAT IS AT A SLAG TEMPERATURE OF ABOUT 150*C, AND DISCONTINUING THE APPLICATION OF HEAT AT THAT INITIATION POINT SO THAT THE TEMPERATURE OF THE TITANIFEROUS SLAG CONTINUES TO RISE DUE TO THE HEAT GENERATED BY THE EXOTHERMIC OXIDATION OF THE TRIVALENT TITANIFEROUS; AND B. REAPPLYING HEAT TO THE TITANIFEROUS SLAG AFTER THE TEMPERATURE OF THE SLAG REACHES A MAXIMUM, WHEREBY THE TEMPERATURE OF THE TITANIFEROUS SLAG IS MAINTAINED WITHIN A RANGE OF FROM ABOUT 300*C TO ABOUT 450*C UNTIL THE DESIRED REDUCTION OF THE TRIVALENT TITANIUM CONTENTS IS ACHIEVED.
 2. The process of claim 1 wherein the oxygen is provided by air.
 3. The process of claim 1 wherein the titaniferous slag has a particle size within the range of from about 4 to about 325 mesh.
 4. The process of claim 1 wherein the titaniferous slag has a particle size of at least 75 percent-325 mesh.
 5. The process of claim 1 wherein the titaniferous slag has a particle size of 80% -325 mesh and the period for maintaining the temperature of the titaniferous slag of from about 300* to about 450*C is from about 1 hour to about 5 hours.
 6. The process of claim 1 wherein the titaniferous slag has a particle size of 80 percent-325 mesh, the oxygen is provided by air, and the period for maintaining the temperature of the titaniferous slag of from about 300* to about 450*C is from about 1 hour to about 5 hours. 